Gasoline with added detergent will cost a few more cents per gallon than fuel without these additives, but will do a much more superior job of preventing deposits from building up in the engine, according to AAA.

In testing the quality of gasoline sold by retailers, AAA determined that fuels that did not meet Top Tier standards resulted in an average of 19 times more engine deposits than fuels that met these standards. These carbon deposits can impede fuel economy, increase emissions, and negatively affect performance, especially in new vehicles.

"AAA was surprised to learn the extent to which detergent additives impact gasoline quality," said John Nielsen, managing director of AAA's Automotive Engineering and Repair. "As advertised, tested Top Tier gasolines kept engines remarkably cleaner than other fuels we tested."

In 1996, the Environmental Protection Agency mandated that all gasoline sold in the United States must have a minimum level of detergent to guard against problems caused by carbon deposits. However, some automakers believe the minimum level is not enough to guarantee optimum vehicle performance, fuel economy, or emissions levels.

The Top Tier designation was established to create more stringent standards for engine cleanliness. These specifications are supported by eight automakers, and 46 different retail brands currently meet Top Tier standards.

To test the effects of different types of gasoline, AAA selected a south Texas market where the available Top Tier and non-Top Tier brands represented the types of gasoline sold in the majority of the United States. Three Top Tier brands and three non-Top Tier brands were selected.

Premium gasoline was used for the testing to account for the fact that some non-Top Tier brands may include detergent additives in this grade of fuel. However, Top Tier retailers are required to use detergent additives in all fuel grades.

An independent International Standards Organization 17025 certified engine testing lab was used to measure deposits on an engine's intake valves and combustion chambers. Engines were run continuously for 100 hours, equal to about 4,000 miles of driving, before engine deposits were measured.

Engines that used gasoline meeting Top Tier standards had an average of 34.1 milligrams of deposits per engine valve. By contrast, those that used non-Top Tier gasoline averaged 660.6 milligrams of deposits per engine valve.

AAA says that engine deposits can cause performance issues such as rough idling, hesitation during acceleration, knocking or pinging, a 2 to 4 percent reduction in fuel economy, and a 20 to 30 percent increase in carbon monoxide emissions. The organization says drivers should make sure they are using the correct type of fuel as recommended by the manufacturer.

AAA only performed a visual test to see if Top Tier gasoline could clean existing deposits, noting that the cylinder of an engine that had used non-Top Tier fuel for the majority of its life appeared significantly cleaner after operating with 74.8 gallons of Top Tier gasoline. A previous study in 2009 built up engine deposits in multiple vehicles during on-road testing over 10,000 miles, than used fuel with detergent additives for the remaining 5,000 miles; this switch reduced the deposits by 45 to 72 percent.

A survey issued by AAA found that while 63 percent of 1,002 adult respondents believe there is a difference in the quality of gasoline sold by different gas stations, they were unlikely to give serious consideration to buying fuel with detergent additives. Forty-seven percent said they do not regularly buy this type of fuel, while 18 percent said they do not know if the gas they buy typically has detergent additives. Only 12 percent said the availability of a fuel with detergent additives was a primary reason for selecting a gas station.

Respondents were more likely to choose a gas station based on its convenience and prices. Seventy-five percent chose a station based on its location, while 73 percent based their decision on its price and 29 percent chose a station due to its rewards program.

"Americans are six times more likely to choose a gas station based on the price of gasoline rather than the quality of fuel," said Nielsen. "Since Top Tier gasoline is widely available and only an average of three cents more per gallon, AAA urges drivers to reconsider their priorities when selecting a gas station."